An all-in-one strategy for bisulfite-free DNA methylation detection by temperature-programmed enzymatic reactions

The fragmentation and low concentration of cell-free DNA (cfDNA) pose higher challenges for the cfDNA methylation detection technologies. Conventional bisulfite conversion-based methods are inadequate for cfDNA methylation analysis due to cumbersome operation and exacerbating cfDNA degradation. Herein, we proposed temperature-programmed enzymatic reactions for cfDNA methylation analysis in a single tube. Endonuclease was used to mildly recognize DNA methylation to avoid the degradation of cfDNA. And two stages of amplifi-cation reactions significantly improved the detection sensitivity for GC-rich sequence. With vimentin as the target, the detection sensitivity was 10 copies of methylated DNA. Meanwhile, the proposed method can accurately quantify the methylation level of target sequence from 1000-fold of unmethylated DNA background. Further, the methylated vimentin gene in 20 clinical plasma samples was successfully detected. The results shown significant differences in methylation levels of the vimentin gene between healthy volunteers and colorectal cancer patients. These results lead us to believe that the proposed method has great application potential for DNA methylation analysis as a complement to bisulfite conversion-based methods.

Automated summary

This paper proposes a temperature-programmed enzymatic reaction method for cfDNA methylation analysis in a single tube. The method uses endonuclease to mildly recognize DNA methylation to avoid cfDNA degradation, and two stages of amplification reactions significantly improve detection sensitivity for GC-rich sequences. The method accurately quantifies the methylation level of the target sequence and successfully detects the methylated vimentin gene in 20 clinical plasma samples. The results suggest that the proposed method has great application potential as a complement to bisulfite conversion-based methods for DNA methylation analysis.